Inerting method for preventing and/or extinguishing fire as well as inerting system to realize the method

ABSTRACT

The invention relates to an inerting method as well as an inerting system ( 1 ) to set and/or maintain a reduced oxygen content in an enclosed room ( 2 ), wherein a gas separation system ( 3.1, 4.1; 3.2, 4.2; 3.3, 4.3 ) is provided which separates off at least a portion of the oxygen from an initial gas mixture provided in a mixing chamber ( 6 ) and by so doing, provides a nitrogen-enriched gas mixture. In order to optimize the operation of the inerting system ( 1 ), the invention provides for a portion of the air to be withdrawn from the enclosed room ( 2 ) and admixed with fresh air in the mixing chamber ( 6 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Nonprovisional Application Ser.No. 13/323,110, filed Dec. 12, 2011, which application further claimspriority to European Application No. 10 194 584.8 filed Dec. 10, 2010,the contents of both of which as are hereby incorporated by reference intheir entirety.

BACKGROUND

1. Technical Field

The present invention relates to an inerting method for preventingand/or extinguishing fire in which in a predefinable oxygen contentwhich is lower than normal ambient air is set and maintained in thespatial atmosphere of an enclosed room.

2. Description of Related Art

The invention further relates to an inerting system to set and/ormaintain a predefinable oxygen content in the spatial atmosphere of anenclosed room which is reduced compared to the normal ambient air,wherein the inerting system comprises a gas separation system whichseparates off at least a portion of the oxygen from an initial gasmixture containing nitrogen and oxygen and by so doing, provides anitrogen-enriched gas mixture at the outlet of the gas separationsystem, and wherein the inerting system comprises a supply line systemfor supplying the nitrogen-enriched gas mixture to the enclosed room.

An inerting system of the above type particularly relates to a system toreduce the risk of and extinguish fires in a protected room subject tomonitoring, wherein the protected room is continuously rendered inertfor the purpose of preventing or controlling fire. The mode of action ofsuch an inerting system is based on the recognition that the risk offire in enclosed rooms can be countered by continuously lowering theconcentration of oxygen in the respective area to a value of e.g.approximately 12-15% by volume in normal cases. At such an oxygenconcentration, most combustible materials can no longer ignite. The mainareas of application are in particular IT areas, electrical switchgearand distributor compartments, enclosed facilities as well as storageareas for high-value commodities.

A method as well as a device of the type cited at the outset is knownfrom the EP 2 204 219 A1 printed publication. A return system isemployed here to withdraw a portion of the ambient air from within theenclosed room and feed it to a mixing chamber. Fresh air is added to theportion of air withdrawn from the room in the mixing chamber. The gasmixture thus produced (initial gas mixture) is fed to a compressor to becompressed there and then channeled to a nitrogen generator. Thenitrogen generator separates off at least a portion of the oxygen fromthe initial gas mixture provided, thus producing a nitrogen-enriched gasmixture at the outlet of the nitrogen generator. This nitrogenated gasmixture is thereafter piped into the enclosed room in order to lower theoxygen content of the room's spatial atmosphere to a predeterminedinerting level or to maintain it at a preset inerting level.

In practice, the method of returning oxygen-reduced air employed inprinted publication EP 2 204 219 A1 to enable a more effective nitrogengeneration for fire protection purposes calls for a return method whichis adapted as optimally as possible to the gas separation systememployed. Care must in particular be taken that the initial gas mixtureprovided in the mixing chamber is always in an optimized state for thegas separation system to be employed. This requirement is especiallyapplicable when a plurality of nitrogen generators with respectivelyassociated compressors are employed as the gas separation system. Caremust then in particular be taken that the respective suction action ofeach individual nitrogen generator has no impact on any of the othernitrogen generators. This method has to factor in that a nitrogengenerator which uses membrane technology to separate gases needs toexhibit a constant suction action. On the other hand, when a nitrogengenerator is employed which makes use of the above-described PSAtechnology or the above-described VPSA technology to separate gases, thefact that such a nitrogen generator can operate with pulsed suctionaction needs to be considered.

Particularly in large-volume areas such as for instance warehouses, itis frequently desired to use a plurality of nitrogen generators inparallel for setting and maintaining a predefined or predefinableinerting level, whereby it can occur that the nitrogen generators arebased on different gas separation technologies. Such a case requires acostly and independent return line for each nitrogen generator from theenclosed room to the respective nitrogen generator in order to ensurethe optimum operation of each nitrogen generator. This requirement leadsto a relatively complex structure to the inerting system.

Starting from this problem as posed, the present invention is based onthe task of further developing the inerting system known from the EP 2204 219 A1 printed publication, respectively the inerting method knownfrom the EP 2 204 219 A1 printed publication, such that a predefinedinerting level can be set and maintained in the enclosed room in thesimplest yet most efficient manner possible.

According to a first aspect of the invention related to the inertingmethod, an initial gas mixture containing oxygen, nitrogen and othercomponents as applicable is provided in a mixing chamber, wherein a gasseparation system separates off at least a portion of the oxygen fromthis initial gas mixture provided and by so doing, a nitrogen-enrichedgas mixture is provided at the outlet of the gas separation system, andwherein this nitrogen-enriched gas mixture is piped into the spatialatmosphere of the enclosed room. A return line system connecting theenclosed room to the mixing chamber is provided to supply the initialgas mixture, wherein a fan mechanism is further provided to withdraw aportion of the ambient air from within the enclosed room, preferably inregulated manner, and feed it to the mixing chamber, wherein thewithdrawn portion of the room's air is admixed with fresh air,preferably in regulated manner, by means of a fan mechanism provided inthe fresh air-supply line system connected to the mixing chamber.

A further aspect of the invention with respect to the method providesfor the fan mechanism provided in the return supply line system to becontrolled such that the volume of air withdrawn from the room per unitof time and fed to the mixing chamber be set such that the differencebetween the pressure prevailing in the mixing chamber and the pressureof the external ambient atmosphere does not exceed a predefined orpredefinable upper threshold nor fall short of a predefined orpredefinable lower threshold.

A further aspect of the invention with respect to the method providesfor the fan mechanism provided in the fresh air supply line system to becontrolled such that the volume of fresh air mixed with the withdrawnvolume of room air per unit of time is set such that the differencebetween the pressure prevailing in the mixing chamber and the pressureof the external ambient atmosphere does not exceed a predefined orpredefinable upper threshold nor fall short of a predefined orpredefinable lower threshold.

A further aspect of the invention relating to the inerting systemprovides for the inerting system to further comprise a mixing chamber,preferably a mixing chamber configured as a mixing tube, which serves toprovide the initial gas mixture, wherein a first line system opens intothe mixing chamber, with a portion of the spatial air from inside theenclosed room being withdrawn and fed to the mixing chamber through saidfirst line system, and wherein a second line system opens into themixing chamber, with fresh air being supplied to the mixing chamberthrough said second line system.

A further aspect of the invention with respect to the inerting systemprovides for the inerting system to further comprise a first fanmechanism controllable by a control unit in the first line system and asecond fan mechanism system controllable by the control unit in thesecond line.

A further aspect of the invention with respect to the inerting systemprovides for the control unit of an inerting system provided with such acontrol unit to be designed so as to control the first fan mechanismsuch that the amount of air withdrawn from the room per unit of time andfed to the mixing chamber by means of said first fan mechanism can beset such that the difference between the pressure prevailing in themixing chamber and the pressure of the external ambient atmosphere doesnot exceed a predefined or predefinable upper threshold nor fall shortof a predefined or predefinable lower threshold.

A further aspect of the invention with respect to the inerting systemprovides for the control unit of an inerting system provided with such acontrol unit to be designed so as to control the second fan mechanismsuch that the volume of fresh air admixed to the spatial air withdrawnfrom the room per unit of time by means of said second fan mechanism canbe set such that the difference between the pressure prevailing in themixing chamber and the pressure of the external ambient atmosphere doesnot exceed a predefined or predefinable upper threshold nor fall shortof a predefined or predefinable lower threshold.

A further aspect of the invention with respect to the inerting systemprovides for the inerting system to comprise a control unit which isdesigned to control the gas separation system such that the residualoxygen content of the nitrogen-enriched gas mixture is changed as afunction of the oxygen content prevailing in the spatial atmosphere ofthe enclosed room at that respective moment.

The resulting preventative or extinguishing effect of this inertingmethod is based on the principle of oxygen displacement. As is generallyknown, normal ambient air consists of about 21% oxygen by volume, about78% nitrogen by volume and about 1% by volume of other gases. In orderto be able to effectively reduce the risk of a fire breaking out in aprotected room, the concentration of oxygen in the respective room islowered by introducing inert gas such as e.g. nitrogen. For most solids,a fire-extinguishing effect is known to occur when the percentage ofoxygen falls below 15% by volume. Depending on the flammable materialscontained within a protected room, a further lowering of the oxygenpercentage to e.g. 12% by volume may be necessary. Thus, continuouslyrendering a protected room inert will also effectively minimize the riskof a fire breaking out in said protected room.

The inventive method, inerting system respectively, capitalizes on theknowledge that the nitrogen purity of the nitrogenated gas mixtureprovided at the outlet of the gas separation system, respectively theresidual oxygen content of the nitrogenated gas mixture provided at theoutlet of the gas separation system, has an effect on the so-called“drawdown time.” The term “drawdown time” refers to the length of timerequired to set a predefined inerting level in the spatial atmosphere ofthe enclosed room.

The specific knowledge capitalized on herein is that as nitrogen purityincreases, the air factor of the gas separation system risesexponentially.

The term “air factor” refers to the ratio of the volume of initial gasmixture pro-vided the gas separation system per unit of time to thevolume of nitrogenated gas provided at the outlet of the gas separationsystem per unit of time. A nitrogen generator will usually allow thearbitrary selection of any nitrogen purity desired at the outlet of thegas separation system, with this value able to be set on the nitrogengenerator itself. Generally speaking, the lower the nitrogen purity isset, the lower the operating costs for the nitrogen generator will be.In particular, the compressor then only needs to run for a comparativelyshorter period of time when providing a nitrogenated gas mixture at theset nitrogen purity at the outlet of the gas separation system.

With respect to the costs incurred to operate the inerting system toinert the room, however, other additional factors need to be taken intoaccount. These particularly include the purge factors involved indisplacing the oxygen in the spatial atmosphere of the enclosed room bymeans of the nitrogen-enriched gas mixture provided at the outlet of thegas separation system until the predefined inerting level is reached,respectively maintained. These purge factors particularly include theamount of nitrogenated gas provided by the gas separation system perunit of time, the spatial volume of the enclosed room, and thedifference between the oxygen content prevailing in the spatialatmosphere of the enclosed room at that respective moment versus theoxygen content corresponding to the predefined inerting level. To behereby considered is that in terms of the drawdown time, the nitrogenpurity of the gas mixture provided at the outlet of the gas separationsystem, respectively the residual oxygen content of the nitrogenated gasmixture, likewise plays a crucial role, since the purging operation goesfaster the lower the residual oxygen content in the nitrogenated gasmixture.

The term “gas separation system” as used herein is to be understood as asystem which can effect the separation of an initial gas mixturecomprising at least the components of “oxygen” and “nitrogen” into anoxygen-enriched gas as well as a nitrogen-enriched gas. The functioningof such a gas separation system is usually based on the effect of gasseparation membranes. The gas separation system used in the presentinvention is primarily designed to separate oxygen from the initial gasmixture. This type of gas separation system is frequently also referredto as a “nitrogen generator.”

This type of gas separation system makes use of a membrane module or thelike, for example, whereby the different components contained in theinitial gas mixture (e.g. oxygen, nitrogen, noble gases, etc.) diffusethrough the membrane at different speeds based on their molecularstructure. A hollow fiber membrane can be used as the membrane. Oxygen,carbon dioxide and hydrogen have a high diffusion rate and because ofthat, escape from the initial gas mixture relatively quickly whenpassing through the membrane module. Nitrogen having a low diffusionrate percolates through the hollow fiber membrane of the membrane modulevery slowly and thereby concentrates when passing through said hollowfiber/membrane module. The nitrogen purity, the residual oxygen contentrespectively, of the gas mixture exiting the gas separation system isdetermined by the flow velocity. Varying the pressure and the volumetricflow rate allows the gas separation system to be adjusted to therequired nitrogen purity and necessary volume of nitrogen. Specifically,the purity of the nitrogen is regulated by the speed at which the gaspasses through the membrane (dwell time).

The separated oxygen-enriched gas mixture is usually concentrated anddischarged into the environment at atmospheric pressure. The compressed,nitrogen-enriched gas mixture is provided at the outlet of the gasseparation system. An analysis of the product gas composition ensues bymeasuring the residual oxygen content in volume percent. The nitrogencontent is calculated by subtracting the measured residual oxygencontent from 100%. In so doing, it needs to be considered that althoughthis value is designated as the nitrogen content or the nitrogen purity,it is in fact the inert content as this component is not only comprisedof just nitrogen but also other gas components such as for example noblegases.

The gas separation system, nitrogen generator respectively, is usuallyfed compressed air which has been purified by upstream filter units. Itis in principle conceivable to use a pressure swing process (PSAtechnology) utilizing two molecular sieve beds to provide thenitrogen-enriched gas, wherein the two sieves are alternatingly switchedfrom a filter mode to a regeneration mode, thereby yielding the flow ofnitrogen-enriched gas.

As long as it is not imperative to have a continuous flow ofnitrogen-enriched gas at the outlet of a pressure swing-operatingnitrogen generator, just one molecular sieve bed can also be used whichis alternatingly switched into an adsorption mode upon the applicationof pressure, during which the nitrogen-enriched gas is provided at theoutlet, and thereafter into a desorption mode at lower pressure duringwhich the oxygen-enriched air within the proximity of the molecularsieve bed can be purged off.

When a nitrogen generator utilizes for example a membrane technology,the process capitalizes on the general knowledge that different gasesdiffuse through materials at different speeds. In the case of nitrogengenerators, the different diffusion rates of the principal components ofair; i.e. nitrogen, oxygen and water vapor, are used to generate a flowof nitrogen, respectively nitrogen-enriched air. In detail, totechnically realize a membrane technology-based nitrogen generator, aseparation material through which water vapor and oxygen can readilydiffuse, but which only affords a low diffusion rate for nitrogen, isapplied to the outer surfaces of the hollow fiber membranes. When airflows through the inside of such a treated hollow fiber, the water vaporand oxygen quickly diffuse outward through the hollow fiber wall whilethe nitrogen is largely retained within the fiber such that a strongconcentration of nitrogen builds up during passage through the hollowfiber. The effectiveness of this separation process essentially dependson the flow rate in the fiber and the pressure differential over thehollow fiber wall. With a decreasing flow rate and/or a higher pressuredifferential between the interior and the exterior of the hollow fibermembrane, the purity of the resultant nitrogen flow increases. Generallyspeaking, a membrane technology-based nitrogen generator can thusregulate the degree of nitrogenization to the nitrogenated air providedby the nitrogen generator as a function of the dwell time of thecompressed air provided by the compressed air source in the airseparation system of the nitrogen generator.

If, on the other hand, the nitrogen generator is for example based onPSA technology, specially-treated activated charcoal makes use of thedifferent binding rates of the atmospheric oxygen and atmosphericnitrogen. The structure of the activated charcoal employed is therebychanged such that a large number of micropores and submicropores (d<1nm) develop over an extremely large surface area. At this pore size, theoxygen molecules of the air diffuse into the pores substantially fasterthan the nitrogen molecules such that the air in the proximity of theactivated charcoal becomes enriched with nitrogen. A PSAtechnology-based nitrogen generator can thus—as is also the case with amembrane technology-based generator—regulate the degree ofnitrogenization to the nitrogenated air provided by the nitrogengenerator as a function of the dwell time of the compressed air providedby the compressed air source in the nitrogen generator.

As described above, these types of PSA technology-based nitrogengenerators need to be alternately operated in an adsorption mode and adesorption mode, whereby pressure has to be applied to the molecularsieve bed during the adsorption mode (filter mode) in order to ensuresufficient diffusion of oxygen molecules in the pores of the activatedcharcoal (carbon granules, CMS) for the generating process. Compared tothe higher sieve bed pressure versus the ambient pressure during theadsorption phase, the pressure is reduced during the subsequentdesorption phase (purge or regeneration phase) in order to enableeffective purging of the carbon granules.

Standard PSA nitrogen generators, which are also called pressure swingadsorption generators for this reason, use a pressure levelsubstantially corresponding to the ambient pressure during theregeneration cycle (desorption phase). Compared to such standardpressure swing adsorption generators, so-called vacuum pressure swingadsorption generators (VPSA technology) are of more complexconfiguration, their desorption process is thereby intensified,respectively shortened, by the fact that not only is the pressurereduced to the level of the ambient pressure but also a pressureapproaching a vacuum pressure level, which is lower than the ambientpressure, is actively established in the proximity of the molecularsieve bed to be regenerated. To do so, it is then necessary to provide,in addition to the increased pressure level provided by the compressor,also a corresponding reduced pressure approaching a vacuum pressurelevel, for which a vacuum source is usually needed. Such a vacuum sourcecan be in the form of a vacuum pump, for example.

As indicated above, the inventive solution makes use of the knowledgethat the air factor of the gas separation system increases exponentiallywith increasing nitrogen purity on the one hand and, on the other, thatin order to set a predefined inerting level, the compressor used in theinerting system has to run for a longer period of time the lower thedifference is between the oxygen content prevailing in the spatialatmosphere of the enclosed room at that respective moment and theresidual oxygen content in the nitrogenated gas mixture. It is hereby tobe taken into account that the power consumption of the inerting systemis virtually directly proportional to the length of time the drawdownprocess takes to render a room inert, whether when setting the room at afixed residual oxygen content or when lowering to a new reduced level,since the compressor upstream of the gas separation system is digitallydriven to its operating point at optimum efficiency.

It thus remains to be noted that—when a lower value of e.g. only 90% byvolume is selected for the nitrogen purity—the inert gas system has torun for a relatively long period of time in order to set an inertinglevel. Should the nitrogen purity value be raised for example to 95% byvolume, the difference between the oxygen content of the inerting levelto be set and the residual oxygen content of the gas mixture provided atthe outlet of the gas separation system likewise increases, whichthereby reduces the amount of runtime the compressor needs to set aninerting level, and thus lowers the power consumption of the inertingsystem. However the circumstance of increasing the nitrogen purity atthe outlet of the gas separation system inevitably also increases theair factor. The circumstance has a negative effect on the runtime of thecompressor necessary to set an inerting level, respectively the powerconsumption of the inerting system. This negative effect prevails if theincrease in the air factor due to increasing the nitrogen purity becomesappreciable.

Unlike with the usual systems known from the prior art where a fixedvalue is selected for the nitrogen purity of the gas separation system,the present invention is based on an inerting system in which, when theenclosed room is being rendered inert, the residual oxygen contentprovided at the outlet of the gas separation system and thenitrogen-enriched gas mixture is preferably automatically or selectivelyadjusted to the oxygen content prevailing at that respective moment inthe spatial atmosphere of the enclosed room in order to thus set thenitrogen purity of the gas separation system to a value which isoptimized in terms of the time required.

The phrase “time-optimized nitrogen purity value” as used herein refersto the nitrogen purity of the gas separation system, the residual oxygencontent respectively, provided at the outlet of the gas separationsystem and the nitrogen-enriched gas mixture with which a definedinerting system, in which the volume of nitrogenated gas mixture able tobe provided per unit of time is constant, assumes a minimum time periodfor lowering from a current oxygen content to a predefined oxygencontent corresponding to a given inerting level.

Being able to set the volume of room air withdrawn from the room perunit of time and fed to the mixing chamber and/or the volume of freshair added to the withdrawn portion of the room air per unit of time suchthat the difference between the pressure prevailing in the mixingchamber and the ambient atmospheric pressure does not exceed apredefined or predefinable upper threshold nor fall short of apredefined or predefinable lower threshold ensures that the initial gasmixture provided at the outlet of the mixing chamber is always in adefined state and optimally adapted to the gas separation system. Theinventive solution in particular allows gas separation systems utilizinga plurality of nitrogen generators, whereby said plurality of nitrogengenerators can also be based on differing gas separation technologies.Particularly ensured with the inventive solution is that the respectivesuction action of the plurality of nitrogen generators applicablyemployed will not interact with the other nitrogen generators provided.It is therefore readily feasible for the inventive solution to also beemployed as a fire extinguishing system or a fire prevention measure inlarge-volume rooms, for instance warehouses, by using multiple andpotentially different nitrogen generators therein for the gasseparation, without the need for a costly, independent and regulatedreturn line for each nitrogen generator from the protected room to therespective nitrogen generator. Accordingly, the adapted return methodproposed by the inventive solution avoids increased expenditure inrealizing the inventive inerting system.

The solution according to the invention in particular also lowers theoperational costs required to produce the inerting effect in a simple torealize yet effective manner, in particular also in the case ofrelatively large-volume rooms such as warehouses, for example.

A further aspect of the invention provides for the upper pressuredifferential threshold to be 1.0 mbar, preferably 0.5 mbar, whereby thelower pressure differential threshold is preferably 0.0 mbar. Having thedifference between the pressure prevailing in the mixing chamber and theexternal atmospheric pressure being within this indicated range alwaysensures that the respective suction action of the nitrogen generatorsemployed (a constant suction action for a nitrogen generator which usesmembrane technology for the gas separation or a pulsed suction actionfor a nitrogen generator which uses PSA or VPSA technology for the gasseparation) will be a non-interacting action. Of course other values arealso conceivable for the upper and/or lower threshold.

A further aspect of the invention provides for a control unit-regulatedfirst fan mechanism in a first line system via which a portion of thespatial air contained within the enclosed room is withdrawn from theroom in a manner regulated by said control unit and fed to the mixingchamber. Of further advantage is the providing of a second controlunit-regulated fan mechanism in a second line system, via which freshair is supplied to the mixing chamber in regulated fashion. The controlunit should thereby be designed to control the first and/or second fanmechanism such that the volume of spatial air withdrawn from the roomper unit of time is identical to the volume of the nitrogen-enriched gasmixture which is supplied to the spatial atmosphere of the enclosed roomper unit of time. Providing the correspondingly controllable fanmechanisms can further maintain the difference between the pressureprevailing in the mixing chamber and the external ambient atmosphericpressure (within a certain control range) at a predefined orpredefinable value in a simple to realize yet effective manner. Thisthus ensures that the initial gas mixture is provided to therespectively utilized nitrogen generators of the gas separation systemin an optimally adapted state.

According to a further aspect of the invention, the volume of fresh airwhich is admixed with the spatial air withdrawn from the room in themixing chamber per unit of time is selected such that the volume ofspatial air withdrawn from the room per unit of time is identical to thevolume of the nitrogen-enriched gas mixture which is piped into thespatial atmosphere of the enclosed room per unit of time. This therebyensures that no excess or negative pressure will develop by introducingthe nitrogenated gas mixture into the spatial atmosphere of the enclosedroom or by the discharging/return of the spatial air from the enclosedroom respectively.

To provide the initial gas mixture, a further aspect of the inventionprovides for a mixing section into which open the first line system,through which a portion of the air contained in the enclosed room iswithdrawn from the room in regulated manner, and the second line system,by way of which fresh air is supplied in regulated manner, preferably bymeans of a Y-connector. This mixing section is either integrated intothe mixing chamber or upstream of the mixing chamber. The mixing sectionserves to mix the spatial air withdrawn from the enclosed room with thefresh air as supplied and is configured—in order to ensure optimummixing—so that a turbulent flow will occur in the mixing section. Tothis end, it is conceivable to correspondingly reduce the mixingsection's effective flow cross-section such that a flow rate is set forthe fresh air introduced into the mixing section and the return room airlikewise introduced into the mixing section which is greater than thecharacteristic Reynolds number-dependent limiting velocity.Alternatively or additionally hereto, it is conceivable to providespoiler elements in the mixing section in order to induce a turbulentflow in said mixing section.

In the latter embodiment cited in which a mixing section is integratedinto the mixing chamber or arranged upstream of the mixing chamber forthe turbulent mixing of the return room air and the supplied fresh air,a further aspect of the invention provides for the mixing section toexhibit a length sufficiently long enough to effect the most completeand even mixing of the return room air and supplied fresh air aspossible. It is particularly preferred here for the mixing section to beof a length which is at least five times that of the mixing section'shydraulic diameter. The hydraulic diameter is a theoretical dimensionfor calculations related to tubes or channels of non-circular crosssections. This term then allows making calculations as with a roundtube. It is the quotient of four times the flow cross section and thewetted perimeter (inner and outer as applicable) of a measurement crosssection.

A further aspect of the invention provides for the gas separation systemto comprise at least one and preferably a plurality of nitrogengenerators each associated with a respective compressor connected to themixing chamber by means of a line system. The residual oxygen contentprovided at the outlet of the nitrogen generator and thenitrogen-enriched gas mixture is adjustable for each nitrogen generatorby means of the control unit. This realization is in particular suitablefor protecting large volume areas such as for instance a warehouse.

A further aspect of the invention provides for the gas separationsystem's at least one nitrogen generator, at least one of the pluralityof nitrogen generators respectively, to be configured as a vacuumpressure swing adsorption generator; i.e. in other words, one whichfunctions according to VPSA technology. In the case of such a vacuumpressure swing adsorption generator, a line system is additionallyprovided between the mixing chamber and at least one inlet of the vacuumpressure swing adsorption generator. A controllable intermediate valvehaving a control connection to the control unit is active in this linesystem. The control unit can thus effect a direct controllableconnection between the mixing chamber and the at least one inlet of thevacuum pressure swing adsorption generator. In conjunction with themethod according to the invention, it is then provided that during thedesorption phase of the vacuum pressure swing adsorption generator andfor example a few seconds before the desorption phase is scheduled toend, for example five seconds before the scheduled end of the desorptionphase, the intermediate valve in the line system connecting the mixingchamber and the nitrogen generator is brought from a closed positioninto an open position allowing passage so that the mixing chamber isdirectly connected to at least one inlet of the vacuum pressure swingadsorption generator prior to the end of the vacuum pressure swingadsorption generator's desorption phase.

A further aspect of the invention provides for the nitrogen generator ofthe gas separation system configured as a vacuum pressure swingadsorption generator to comprise at least one inlet, wherein the atleast one inlet is selectively connected to the pressure side of acompressor or to the suction side of a vacuum source by means of a linesystem.

According to a further aspect of the invention with a nitrogen generatorof the gas separation system configured as a vacuum pressure swingadsorption generator having at least one inlet, the at least one inletof the nitrogen generator is connected to the suction side of the vacuumsource during a desorption phase.

According to a further aspect of the invention with a nitrogen generatorof the gas separation system configured as a vacuum pressure swingadsorption generator, at least one inlet of the nitrogen generator isselectively connected to the mixing chamber by means of a line system.

According to a further aspect of the invention with a nitrogen generatorof the gas separation system configured as a vacuum pressure swingadsorption generator having at least one inlet, the at least one inletof the nitrogen generator is connected to the mixing chamber by means ofa line system to end a desorption phase of the nitrogen generator.

Since a negative pressure prevails at this inlet of the vacuum pressureswing adsorption generator during the desorption phase,nitrogen-enriched air from the mixing container is automaticallyprovided into this inlet of the vacuum pressure swing adsorptiongenerator prior to the end of the desorption phase, which leads forexample to an adsorption bed containing carbon granules (CMS). A passiveincrease in pressure thus occurs in such an adsorption bed (CMScontainer) so that the desorption phase for this vacuum pressure swingadsorption generator can be passively ended without any additionalexpenditure of energy which saves time and energy compared toconventional solutions. Furthermore, when the pressure swing adsorptiongenerator is then thereafter switched into a subsequent adsorptionoperation, such a passive increase in pressure in the adsorption bed(CMS container) enables the vacuum pressure swing adsorption generatorto be switched into adsorption operation possible without the compressorload that would otherwise be necessary to regenerate a pressure in thearea of the adsorption bed for the subsequent adsorption operation whichis closer to the excess pressure subsequently created during theadsorption phase. What this realizes is that the compressor associatedwith the vacuum pressure swing adsorption generator can bring themolecular sieve bed back to the operating pressure in a shorter amountof time, whereby nitrogen is then in turn generated faster at the outletof the vacuum pressure swing adsorption generator. Moreover, because airwhich is already nitrogenated flows from the mixing chamber toward themolecular sieve bed, the oxygen level during the subsequent adsorptionphase already starts at a lower level. The appropriate design to themixing chamber, for example preferably as a long mixing tube, in turnyields advantageous pressure fluctuation-compensating properties so thateven the early end of a pressure equalization procedure in such adesorption phase of the vacuum pressure swing adsorption generator willnot have any impact on for example any other of the plurality ofnitrogen generators. In other words, ensuring the continuednon-interacting operation of all the nitrogen generators employed.

With respect to the mixing chamber employed in the inventive solution, afurther aspect of the invention provides for said mixing chamber toexhibit a volume which is dependent on the number of nitrogen generatorsused in the inerting system and/or on the principle on which thefunctioning of the least one nitrogen generator is based. The volume ofthe mixing chamber is to in particular be selected such that therespective suction action of the nitrogen generators employed will be anon-interacting action for all nitrogen generators.

In accordance with a further aspect of the invention, the mixing chamberis hereby further configured such that the maximum flow rate which canoccur in the mixing chamber is less than 0.1 m/s on average. This isattained by suitably selecting the mixing chamber's hydraulic crosssection.

A further aspect of the invention provides for the residual oxygencontent of the nitrogen-enriched gas mixture, the nitrogen purity of thegas separation system respectively, to preferably be set automaticallyaccording to a predetermined characteristic curve.

A further aspect of the invention provides for such a characteristiccurve to specify the time-optimized behavior of the residual oxygencontent in the nitrogenated gas mixture in relation to the oxygencontent in the spatial atmosphere of the enclosed room, according towhich the inerting process can set a predefinable reduced oxygen contentin the spatial atmosphere of the enclosed room compared to the normalambient air in the shortest amount of time.

The phrase “time-optimized behavior of the residual oxygen content”refers to the time-optimized value of the residual oxygen contentdependent on the oxygen content in the spatial atmosphere of theenclosed room. As indicated above, the time-optimized value of theresidual oxygen content corresponds to the value of the residual oxygencontent to be selected for the gas separation system such that theinerting method can set a predefinable oxygen content in the spatialatmosphere of the enclosed room which is reduced compared to the normalambient air within the shortest amount of time.

The characteristic curve, according to which the residual oxygen contentis set as a factor of the oxygen content prevailing at that respectivemoment in the spatial atmosphere of the enclosed room is predetermined(measured or calculated) for the gas separation system/inerting system.

Since one aspect of the inventive solution relates to the setting of thenitrogen purity of the gas separation system, or the residual oxygencontent in the nitrogen-enriched gas mixture respectively, as a functionof the oxygen content prevailing in the spatial atmosphere of theenclosed room at that respective moment and according to a furtheraspect of the inventive solution, the nitrogen purity of the gasseparation system, the residual oxygen content in the nitrogen-enrichedgas mixture respectively, is automatically set as a function of theoxygen content prevailing in the spatial atmosphere of the enclosed roomat that respective moment so as to thereby be able to render the roominert at the lowest possible operating costs, a further aspect of theinvention provides for either directly or indirectly measuring thecurrent oxygen content in the spatial atmosphere of the enclosed roomcontinuously or at predefined times and/or upon predefined events. Afurther aspect of the invention then further provides for setting theresidual oxygen content in the nitrogen-enriched gas mixture to apredefined, time-optimized value continuously or at predefined timesand/or upon predefined events. This predefined, time-optimized value isto correspond to a residual oxygen content at which the inerting methodcan lower the oxygen content in the spatial atmosphere of the enclosedroom to a predefined drawdown value based on the respectively currentoxygen content within the shortest amount of time possible.

A further aspect of the inventive solution provides not only for thenitrogen purity of the gas separation system to be changed as a functionof the oxygen content prevailing at that respective moment in thespatial atmosphere of the enclosed room, but the oxygen content in theinitial gas mixture is also changed as a function of the oxygen contentprevailing in the enclosed room's spatial atmosphere at that respectivemoment. Doing so makes use of the knowledge that the air factor of thegas separation system can be lowered when the initial gas mixturesupplied to the gas separation system exhibits a reduced oxygen content.

Thus, for the purpose of providing the initial gas mixture, one aspectof the invention provides for the regulated withdrawing of a portion ofthe ambient air from within the enclosed room and the regulatedsupplying of fresh air to the withdrawn portion of the room's air. So asto thereby prevent the pressure inside the enclosed room from changingby the supplying of nitrogen-enriched gas or by the drawing off aportion of its ambient air, the volume of fresh air admixed to theambient air withdrawn from the room is selected such that the volume ofambient air withdrawn from the room per unit of time is identical to thevolume of nitrogen-enriched gas mixture provided at the outlet of thegas separation system and piped into the spatial atmosphere of theenclosed room per unit of time.

The following will make reference to the accompanying drawings indescribing exemplary embodiments of the inventive inerting system.

BRIEF DESCRIPTION OF THE FIGURES

Shown are:

FIG. 1 a schematic view of an inerting system according to a firstembodiment of the present invention;

FIG. 2 a schematic view of an inerting system according to a secondembodiment of the present invention;

FIG. 3 a schematic view of an inerting system according to a thirdembodiment of the present invention;

FIG. 4 a schematic view of an inerting system according to a fourthembodiment of the present invention;

FIG. 5 a graphical illustration of the air factor in relation to thenitrogen purity with an inerting system according to FIG. 1, FIG. 2,FIG. 3 or FIG. 4, as well as a graphical illustration of the drawdowntime in relation to the nitrogen purity, and specifically the loweringof the oxygen content from its original 17.4% by volume to 17.0% byvolume as well as a lowering of the oxygen content from its original13.4% by volume to 13.0% by volume;

FIG. 6 a graphical illustration of the time-optimized nitrogen purity inrelation to the current oxygen content in the spatial atmosphere of theenclosed room with the inerting system according to FIG. 1, FIG. 2, FIG.3 or FIG. 4;

FIG. 7 a graphical illustration of the air factor of the gas separationsystem with the inerting system according to FIG. 1, FIG. 2, FIG. 3 orFIG. 4 compared to the oxygen content of the initial gas mixturesupplied to the gas separation system in order to separate at least aportion of the oxygen from the initial gas mixture and thereby provide anitrogenated gas mixture at the outlet of the gas separation system;

FIG. 8 a graphical illustration of the energy savings which can beachieved by lowering the oxygen content of the enclosed room's spatialatmosphere by means of the inventive solution;

FIG. 9 a schematic view of an inerting system according to a fifthembodiment of the present invention; and

FIG. 10 a schematic view of an inerting system according to a sixthembodiment of the present invention.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

FIG. 1 shows a first exemplary embodiment of an inerting system 1according to the present invention in a schematic representation. Theinerting system 1 depicted serves to set and maintain a predefinableinerting level in the spatial atmosphere of an enclosed room 2. Theenclosed room 2 can be a warehouse, for example, in which the oxygencontent of the room's ambient air is lowered to and maintained at aspecific inerting level of e.g. 12% or 13% by volume of oxygen as apreventive fire protection measure.

The enclosed room 2 is selectively rendered inert automatically by meansof a control unit 5. To this end, the inerting system 1 according to theembodiment depicted in FIG. 1 comprises a gas separation systemconsisting of a compressor 3.1 as well as a nitrogen generator 4.1. Thecompressor 3.1 serves to provide a compressed initial gas mixture to thenitrogen generator 4.1 comprised of at least the components of oxygenand nitrogen. To this end, the outlet of the compressor 3.1 is connectedto the inlet of the nitrogen generator 4.1 by means of a line system17.1 in order to supply the compressed initial gas mixture to thenitrogen generator 4.1. It is conceivable for the initial gas mixture atthe outlet of the compressor 3.1 to be compressed to a pressure of e.g.7.5 to 9.5 bar and preferably 8.8 bar.

The nitrogen generator 4.1 comprises at least one membrane module 19,for example a hollow fiber membrane module, through which the initialgas mixture provided by the compressor 3.1—after having passed throughan appropriate filter 18—is pressed. The different components containedin the initial gas mixture (in particular oxygen and nitrogen) diffusethrough the hollow fiber membrane of the membrane module 19 within saidmembrane module 19 at different rates according to their molecularstructure. The gas separation is thereby based on the known operatingprinciple of nitrogen only percolating through the hollow fiber membranevery slowly at a low diffusion rate and thereby concentrating as itpasses through the hollow fiber membrane of the membrane module 19. Anitrogen-enriched gas mixture is thus provided at the outlet 4 a.1 ofthe nitrogen generator 4.1. This nitrogen-enriched gas mixture is—as isalso the case with the initial gas mixture supplied at the inlet of thenitrogen generator 4.1—in compressed form, wherein passing through theat least one membrane module 19 of the nitrogen generator 4.1 does,however, lead to a drop in pressure of e.g. 1.5 to 2.5 bar.

Although not explicitly depicted in FIG. 1, the oxygen-rich gas mixtureseparated out in the nitrogen generator 4.1 is concentrated anddischarged to the surroundings at atmospheric pressure.

The nitrogen-enriched gas mixture provided at the outlet 4 a.1 of thenitrogen generator 4.1 is fed to the enclosed room 2 through a supplyline 7.1 in order to lower the oxygen content in the spatial atmosphereof the enclosed room 2, respectively to maintain a previously-setdrawdown level in room 2, by adding nitrogen-enriched gas.

A suitable pressure relief can be provided so that the pressure withinthe enclosed room 2 does not change when the nitrogenated gas mixture issupplied. This can be realized for example as independentlyopening/closing pressure relief valves (not shown in FIG. 1). On theother hand, it is however also conceivable for the discharged volume ofambient air to be supplied to a mixing chamber 6 via a return linesystem 9 for the purpose of pressure relief when rendering room 2 inert.

The ambient air discharged from the enclosed room 2 is supplied to themixing chamber 6 via a first inlet 9 a of the return line 9. The mixingchamber 6 further comprises a second inlet 8 a which opens into a supplyline system 8 for supplying fresh air to the mixing chamber 6. Themixing chamber 6 provides the initial gas mixture, which has beencompressed by compressor 3 and from which at least a portion of theoxygen is separated off in the gas separation system (nitrogen generator4.1). For this reason, the outlet of the mixing chamber 6 is connectedto the inlet of the compressor 3.1 by an appropriate line system 15.1.

In detail, a first fan mechanism 11 controllable by control unit 5 isprovided in the return line system 9 and a second fan mechanism 10,likewise controllable by control unit 5, is provided in the fresh airsupply line system 8. Doing so thus ensures that by appropriatelyactuating the respective fan mechanisms 10, 11, the amount of fresh airmixed with the ambient air withdrawn from room 2 will be selected suchthat the volume of air withdrawn from room 2 per unit of time isidentical to the volume of nitrogen-enriched gas mixture provided at theoutlet 4 a.1 of the nitrogen generator 4.1 as piped into the spatialatmosphere of the enclosed room 2 per unit of time.

The inerting system 1 according to the embodiment of the presentinvention depicted schematically in FIG. 1 is characterized by theabove-cited control unit 5 being connected to the correspondinglycontrollable components of the inerting system 1 and designed so as toautomatically control the nitrogen generator 4.1, the gas separationsystem respectively, such that the nitrogenated gas mixture provided atthe outlet 4 a.1 of the gas separation system has a residual oxygencontent which is dependent on the oxygen content prevailing in thespatial atmosphere of the enclosed room 2 at that respective moment. Inparticular, the nitrogen generator 4.1 of the depicted preferredrealization of the inventive inerting system 1 is controlled by means ofthe control unit 5 such that depending on the oxygen content in thespatial atmosphere of the enclosed room 2 as measured by means of anoxygen measuring system 16, the nitrogen-enriched gas mixture will havea residual oxygen content of between 10.00% to 0.01% by volume, whereinthe residual oxygen content of the nitrogen-enriched gas mixturedecreases as the oxygen content in the spatial atmosphere of theenclosed room 2 decreases.

To this end, the inventive inerting system 1 further comprises, inaddition to the above-mentioned oxygen measuring system 16 for measuringor determining the current oxygen content in the spatial atmosphere ofthe enclosed room 2, a residual oxygen content measuring system 21 formeasuring the residual oxygen content in the nitrogenated gas mixtureprovided at the outlet 4 a.1 of the nitrogen generator 4.1, respectivelyfor determining the nitrogen purity of the gas mixture provided at theoutlet 4 a.1 of the nitrogen generator 4.1. Both measuring systems 16,21 are correspondingly connected to the control unit 5.

FIG. 2 shows a schematic view of an inerting system 1 according to asecond embodiment of the present invention. The inerting system 1according to the second embodiment is particularly suited to setting andmaintaining a predefined inerting level in an air-conditioned room suchas a cold storage room or a refrigerated warehouse, for example, aseconomically as possible. The design and functioning of the inertingsystem 1 according to the embodiment depicted in FIG. 2 substantiallycorresponds to the design and functioning of the inerting systemdescribed above with reference to FIG. 1 so that to avoid repetition,the following will only address the differences.

To enable the most economic inerting of an air-conditioned room 2possible, it is preferable to provide a heat exchanger system 13 in thereturn line system 9 between the room 2 and the mixing chamber 6, asdepicted in FIG. 2. It is further advantageous for the return linesystem 9 to be at least partly sheathed in an appropriate thermalinsulation 20—as indicated in FIG. 2—so as to prevent freezing of thereturn line system 9 when the chilled ambient air withdrawn from theenclosed room 2 is fed to the heat exchanger system 13 via the returnline system 9 before said air is then piped into the mixing chamber 6.The heat exchanger system 13 can comprise a booster fan 14 as needed sothat the ambient air can be withdrawn from the spatial atmosphere of theenclosed room 2 without a drop in pressure.

The heat exchanger system 13 thereby serves to utilize at least aportion of the waste heat resulting from the operation of the compressor3.1 in order to accordingly warm the cooled ambient air withdrawn fromthe room. Different systems are used for the heat exchanger system 13,such as for example a fin coil heat exchanger which transfers at least aportion of the thermal energy of the exhaust air from compressor 3.1 tothe air withdrawn from the room by means of a heat-exchange medium suchas e.g. water so as to raise the temperature of the withdrawn ambientair to a moderate temperature of for example 20° C., which isadvantageous in terms of the functioning and the efficiency of thenitrogen generator 4.1.

After the ambient air withdrawn from the enclosed room 2 has filteredthrough the heat exchanger system 13, it is fed to the mixing chamber 6via a first inlet 9 a of the return line system 9. The mixing chamber 6further comprises a second inlet 8 a, into which a supply line system 8opens for supplying fresh air to the mixing chamber 6. The mixingchamber 6 provides the initial gas mixture, compressed by compressor 3.1and from which at least a portion of the oxygen has been separated offin the gas separation system (nitrogen generator 4.1). For this reason,the outlet of the mixing chamber 6 is connected to the inlet of thecompressor 3.1 by means of an appropriate line system 15.

FIG. 3 shows a schematic view of an inerting system 1 according to athird embodiment of the present invention. The design and functioning ofthe inerting system 1 according to the embodiment depicted in FIG. 3substantially corresponds to the design and functioning of the inertingsystem described above with reference to FIG. 1 so that to avoidrepetition, the following will only address the differences.

As FIG. 3 shows, the mixing chamber of the embodiment depicted thereinis realized as a filter 6′. The mixing chamber realized as a filter 6′thus fulfills two functions: on the one hand, it serves to provide theinitial gas mixture, and does so by mixing the fresh air supplied by thefresh air supply line system with the ambient air withdrawn from room 2supplied by the return line system 9. On the other hand, the mixingchamber realized as filter 6′ serves to filter the provided initial gasmixture prior to it being compressed by means of compressor 3.1. Thisthus dispenses with the need for an additional filter at the inlet ofcompressor 3.1.

A fourth exemplary embodiment of the inventive inerting system 1 will bedescribed below making reference to the representation provided in FIG.4.

The design and functioning of the inerting system 1 according to thefourth embodiment is essentially identical to the embodiment describedabove with reference to the FIG. 1 depiction, albeit the embodimentaccording to FIG. 4 makes use of a plurality of nitrogen generators 4.1,4.2 and 4.3 connected in parallel. Each nitrogen generator 4.1, 4.2, 4.3is respectively associated with a compressor 3.1, 3.2, 3.3 which isconnected to the mixing chamber 6 by means of a corresponding linesystem 15.1, 15.2, 15.3 so as to suction off the necessary initial gasmixture from the mixing chamber 6 for the associated nitrogen generator4.1, 4.2, 4.3 and to compress it to the pressure value required for theoptimum operation of the respective nitrogen generator 4.1, 4.2, 4.3.Each nitrogen generator 4.1, 4.2, 4.3 utilized in the inerting system 1according to the embodiment depicted in FIG. 4 is connected to theenclosed room 2 by means of a corresponding supply line 7.1, 7.2, 7.3.Hence, the gas separation system depicted in the FIG. 4 embodiment isformed by the “nitrogen generator 4.1, 4.2, 4.3” components and theassociated “compressor 3.1, 3.2, 3.3” components.

As with the embodiments of the inventive solution described above withreference to the representations provided in FIGS. 1 to 3, theembodiment according to FIG. 4 also makes use of a return line 9. Asdepicted, a first fan mechanism 11 is provided in the return line 9which can be correspondingly controlled by the control unit 5 such thata portion of the ambient air can be withdrawn from the enclosed room 2in regulated manner and fed to the mixing chamber 6. A fresh air supplyline 8 is further provided in the embodiment depicted in FIG. 4 tosupply fresh air from an external area 25 to the mixing chamber 6 inregulated manner. To this end, a second fan mechanism 10 controllable bythe control unit 5 is provided in the fresh air supply line 8.

As with the embodiments of the inventive inerting system 1 describedabove, a mixing chamber 6 is also provided in the embodiment depicted inFIG. 4 in order to provide an initial gas mixture comprised of oxygen,nitrogen and other components as applicable. The initial gas mixtureprovided in the mixing chamber 6 is supplied to the respectivecompressors 3.1, 3.2, 3.3 of the gas separation system through thecorresponding line systems 15.1, 15.2, 15.3.

So that the initial gas mixture provided by the mixing chamber 6 is inan optimum state for the respective nitrogen generators 4.1, 4.2, 4.3employed, the embodiment of the inventive inerting system 1 depicted inFIG. 4 provides for a mixing section 12 to be integrated in the mixingchamber 6, although it is not mandatory for said mixing section 12 to beintegrated into the mixing chamber 6, it can also be provided upstreamof the mixing chamber 6.

Specifically, in the embodiment shown in FIG. 4, the return line 9 onthe one hand and the fresh air supply line 8 on the other open intomixing section 12. Although not explicitly shown in FIG. 4, it is herebypreferred for the end 9 a of the return line 9 and the end 8 a of thefresh air supply line 8 to open into mixing section 12 by means of aY-connector preferably situated at the upstream end portion of saidmixing section 12.

The mixing section 12 serves in the optimum mixing of the fresh airsupplied through supply line 8 and the room air supplied through returnline 9. To this end, it is preferred for the mixing section 12 to bedimensioned so that a turbulent flow will be produced within the mixingsection 12. This can for example be achieved by reducing the effectiveflow cross section of mixing section 12 so as to have a flow rate be setin the mixing section 12 which is greater than the limiting velocity toproduce a turbulent flow characteristic of and dependent on thecorresponding Reynolds number. Alternatively or additionally hereto, itis equally conceivable to provide appropriate spoiler elements in themixing section 12 to induce a turbulent flow in said mixing section 12.

As can be noted from the schematic representation provided in FIG. 4,the mixing section 12 exhibits a length sufficiently long enough toeffect the most optimally thorough mixing of the fresh and room airsupplied from the upstream situated end portion to the downstreamsituated end portion of the mixing section. Experimental tests haveshown that it is advantageous for the mixing section 12 to be of alength which is at least five times the effective flow cross section ofthe mixing section 12.

The ambient air return from the enclosed room 2 through return line 9and thoroughly mixed with the supplied fresh air in the mixing section12 is piped into the mixing chamber 6 at the downstream end portion ofthe mixing section 12. In contrast to the mixing section 12, the mixingchamber 6 exhibits a clearly larger effective flow cross section inorder to be able to effect flow abatement. It is particularly necessaryfor the initial gas mixture ultimately provided in the mixing chamber 6to always be in an optimized state for the nitrogen generators 4.1, 4.2,4.3 employed. This in particular means that the difference between thepressure prevailing in the mixing chamber 6 and the external atmosphericpressure does not exceed a predefined or predefinable upper thresholdnor fall short of a predefined or predefinable lower threshold. Inaddition, the maximum flow rate which can occur in the mixing chambershould be less than 0.1 m/s on average.

In order to be able to comply with these conditions in terms of theinitial gas mixture, the embodiment of the inventive inerting system 1depicted in FIG. 4 provides for a pressure sensor 26 inside the mixingchamber 6. Said pressure sensor 26 measures the pressure prevailinginside the mixing chamber 6 continuously or at predetermined timesand/or upon predetermined events and furnishes it to the control unit 5.The control unit 5 compares the pressure value measured in the mixingchamber 6 to the pressure value of the external atmosphere andaccordingly regulates the first and/or second fan mechanism 11, 10 basedon this comparison of the two pressure values in order to ensure thatthe difference between the pressure prevailing in the mixing chamber 6and the external atmospheric pressure does not exceed the predefined orpredefinable upper threshold nor fall short of the predefined orpredefinable lower threshold. For the sake of completeness, it ispointed out that a corresponding pressure sensor 27 is provided in theexternal area 25 to measure the pressure in the external area 25continuously or at predetermined times and/or upon predetermined eventsand furnish it to the control unit 5. Alternatively, the pressure sensor26 could also be a differential pressure sensor.

In the embodiment of the inventive inerting system 1 depicted in FIG. 4,the control unit 5 is designed so as to control the first fan mechanism11 and/or the second fan mechanism 10 such that the difference betweenthe pressure prevailing in the mixing chamber 6 and the externalatmospheric pressure amounts to a maximum of 0.1 mbar and preferably amaximum of 0.5 mbar.

As can be noted from the FIG. 4 depiction, a total of three nitrogengenerators 4.1, 4.2, 4.3 are used for the purpose of gas separation. Itis hereby conceivable for some or all of the nitrogen generators 4.1,4.2, 4.3 to be based on different gas separation techniques. It is thusfor example conceivable for the first nitrogen generator 4.1 to use aseparating membrane for the gas separation. The compressor 3.1associated with the first nitrogen generator 4.1 is then to becorrespondingly adjusted to the applicable pressure to be established atthe inlet of said nitrogen generator 4.1 (e.g. 13 bar). The secondnitrogen generator 4.2 can then for example make use of PSA technologyfor the purpose of the gas separation. The associated compressor 3.2 isto be accordingly configured in this case, whereby it would have tosupply an initial pressure of e.g. 8 bar. The further nitrogen generator4.3 utilized in the embodiment according to FIG. 4 can be a nitrogengenerator based, for example, on VPSA technology. The associatedcompressor 3.3 is then to be configured such that low pressure isprovided at its outlet.

Thus, the gas separation system depicted in the FIG. 4 embodiment makesuse of a combination of different nitrogen generators 4.1, 4.2, 4.3,wherein the compressors 3.1, 3.2, 3.3 respectively associated with thenitrogen generators 4.1, 4.2, 4.3 are adapted to each nitrogengenerator's respective operating mode.

In order to be able to ensure the optimum functioning of the gasseparation system, the mixing chamber 6 needs to be of a large enoughdesign so that no inadmissible pressure fluctuations will occur duringthe operation of the individual compressors 3.1, 3.2, 3.3 and inparticular there will be no interactive impact on the nitrogengenerators 4.1, 4.2, 4.3 employed. As previously noted, the maximumvalue of permissible pressure fluctuations is preferably 1.0 mbar andeven more preferred is 0.5 mbar.

Although not explicitly depicted in FIG. 4, it is preferred for therespective line systems 15.1, 15.2, 15.3 which connect the respectivecompressors 3.1, 3.2, 3.3 to the mixing chamber 6 to open into themixing chamber 6 by way of appropriately dimensioned suction openings soas to be able to prevent any direct dynamic influencing of the intakeair flow. Similarly, the suction openings should be positioned so as tobe accordingly distanced from one another.

The use of the special mixing chamber 6, mixing section 12 respectively,as previously described is not limited to the embodiment of theinventive inerting system 1 depicted in FIG. 4. Rather, it is quiteconceivable to also use the mixing chamber 6, mixing section 12respectively, from FIG. 4 in the embodiments shown in FIGS. 1 to 3 inorder to optimize the operation of the inerting system 1.

As with the above-described embodiments of the inventive inertingsystem, the inerting system 1 according to the FIG. 4 depiction alsoprovides for measuring the oxygen content of the initial gas mixtureprovided in mixing chamber 6 continuously or at predetermined timesand/or upon predetermined events and feeding the measured value to thecontrol unit 5. It is hereto advantageous for a corresponding oxygensensor 22 to be arranged at the downstream end portion of the mixingsection 12.

Providing an oxygen measuring system in return line 9 is of furtheradvantage. However, in place of an oxygen measuring system in the returnline 9, the oxygen content of the ambient air within the enclosed room 2can also be measured. To this end, a an oxygen measuring system 16correspondingly provided in room 2 is used in the embodiment depicted inFIG. 4.

In the embodiment depicted in FIG. 4, in which a plurality of nitrogengenerators 4.1, 4.2, 4.3 are used for the gas separation, it ispreferable to measure the respective flow rates of the gas flows pipedfrom the respective outlets 4 a.1, 4 a.2, 4 a.3 of the nitrogengenerators 4.1, 4.2, 4.3 to the enclosed room 2. As shown, thecorresponding sensors 28.1, 28.2, 28.3 are used in the embodimentdepicted in FIG. 4 for this purpose.

Of further advantage is measuring the flow rate of the return line 9 bymeans of a volumetric flow sensor 29, the flow rate of the fresh airsupply 8 by means of a volumetric flow sensor 30 and the flows rates ofthe initial gas mixtures supplied to the individual compressors 3.1,3.2, 3.3 as applicable. All the measured values are fed to control unit5, which then correspondingly actuates the respective controllablecomponents of the inerting system 1 so as to keep the pressuredifference between the mixing chamber 6 and the external area 25 withinthe permissible control range.

The embodiment depicted in FIG. 4 moreover provides for the control unit5 being able to set the residual oxygen content at each nitrogengenerator 4.1, 4.2, 4.3.

In a preferred realization of the inerting system 1 depictedschematically in FIG. 4, 10 to 11 VPSA nitrogen generators and 2 to 4membrane nitrogen generators are used in parallel, whereby the mixingchamber has a surface area of 10 m×4.3 m.

As set forth in detail below with reference being made to the graphicaldepictions according to FIGS. 5 to 7, appropriately setting the nitrogenpurity of the nitrogen generator(s) 4.1, 4.2, 4.3 utilized, respectivelyappropriately setting the residual oxygen content in the nitrogenatedgas mixture provided at the respective outlet 4 a.1, 4 a.2, 4 a.3 of thegas-separation system, enables a predefined draw-down level to be set inthe spatial atmosphere of the enclosed room in a manner which isoptimized in terms of the time required. Accordingly, the inventivesolution thereby provides for the nitrogen purity of the nitrogengenerator(s) 4.1, 4.2, 4.3 utilized to be set and adjusted as a functionof the oxygen content prevailing in the spatial atmosphere of theenclosed room 2 at that respective moment when said enclosed room 2 isbeing rendered inert.

The nitrogen purity can be changed by varying the dwell time of theinitial gas mixture in the at least one membrane module 19 of thenitrogen generator(s) 4.1, 4.2, 4.3 employed. It is hereby conceivable,for example, to regulate the flow through the membrane module 19 and thebackpressure by means of a suitable control valve 24 at the outlet ofmembrane module 19. A high pressure on the membrane and a long dwelltime (lower flow rate) result in a high nitrogen purity at therespective outlet 4 a.1, 4 a.2, 4 a.3 of the respectively employednitrogen generator 4.1, 4.2, 4.3.

A time-optimized value is preferably selected for the respectivenitrogen purity which enables the inerting system to set and maintain apredefined inerting level in the enclosed room 2 within the shortestamount of time possible. By making use of the appropriate time-optimizedvalues for the nitrogen purity when setting and maintaining a predefinedinerting level in the spatial atmosphere of the enclosed room, it ispossible to reduce the time required for the drawdown process (whetherfor maintaining a fixed residual oxygen content or when lowering to anew drawdown level) and thus also reduce the energy the inerting systemrequires since the compressor 3.1, 3.2, 3.3 is digitally driven (in/out)to its operating point at optimized efficiency.

The inerting system 1 according to the embodiment depicted in FIG. 1, 2,3 or 4 is further characterized by the mixing chamber 6 providing thegas separation system consisting of the compressor 3.1 and the nitrogengenerator 4.1, the gas separation system consisting of compressors 3.1,3.2, 3.3 and nitrogen generators 4.1, 4.2, 4.3 respectively, with aninitial gas mixture which can have a lower oxygen content than theoxygen content of normal ambient air (i.e. approx. 21% by volume).Specifically, the above-cited return line system 9 is provided for thispurpose, same supplying at least a portion of the ambient air of theenclosed room 2 to the mixing chamber 6 through fan mechanism 11 in amanner regulated by control unit 5. Thus, when the oxygen content hasalready been reduced in enclosed room 2, the return line system 9 willsupply the mixing chamber 6 with a gas mixture which isnitrogen-enriched compared to the normal ambient air. This portion ofthe room's air is mixed with supply air in mixing chamber 6 in order toprovide the compressor 3.1 and the nitrogen generator 4.1, compressors3.1, 3.2, 3.3 and nitrogen generators 4.1, 4.2, 4.3 respectively, withthe required volume of initial gas mixture. Since the oxygen content ofthe initial gas mixture influences the air factor of the gas separationsystem, the nitrogen generators 4.1, 4.2, 4.3 as employed respectively,and thus also influences the time-optimized value for the nitrogenpurity of the nitrogen generators 4.1, 4.2, 4.3 as employed, theembodiment of the inventive inerting system 1 depicted in FIG. 1provides for an oxygen measuring system 22 in the line system 15.1between the outlet of the mixing chamber 6 and the inlet of thecompressor 3.1 to measure the oxygen content in the output gas mixture.It is hereto furthermore optionally conceivable to provide correspondingoxygen measuring systems 23A, 23B in the return line system 9, the freshair supply line 8 respectively, in order to measure the oxygen contentin the supply air and in the nitrogen-enriched room air continuously orat predefined times and/or upon predefined events. On the basis of themeasured readings, the composition of the initial gas mixture (inparticular in terms of its oxygen content) can be appropriatelyinfluenced by the appropriate actuating of fan mechanisms 10 and/or 11.

The following will draw reference to the graphical representationsprovided in FIGS. 5 to 7 in describing how the inventive solution of theinerting system 1 depicted schematically in FIGS. 1 to 4 functions. Withrespect to the inerting system 1 depicted schematically in FIGS. 1 to 4,the assumption is to be made that the enclosed room 2 has a spatialvolume of 1000 cubic meters. It is further to be assumed that theinerting system 1 is designed so as to provide a maximum total of 48cubic meters nitrogenated gas per hour at the outlet of the gasseparation system.

FIG. 5 represents a graphical depiction of the air factor for the gasseparation system used in the inerting system 1 schematically depictedin FIGS. 1 to 4 at different nitrogen purities. It is to be accordinglynoted that the air factor increases exponentially as the residual oxygencontent of the nitrogen-enriched gas mixture provided at the outlet ofthe gas separation system decreases. Specifically, the air factor at aresidual oxygen content of 10% by volume (nitrogen purity: 90%) isapproximately 1.5, which means that a volume of 0.67 cubic meters ofnitrogen-enriched gas mixture can be provided at the outlet of the gasseparation system per cubic meter of initial gas mixture. This ratiodeclines with increasing nitrogen purity as can be noted from the FIG. 5graph.

FIG. 5 additionally depicts the air factor trend according to which theregulating drawdown time reacts with increasing nitrogen purity atdifferent nitrogen purities. It is specifically depicted on the one handhow long the compressor or compressors 3.1, 3.2, 3.3 need to run inorder to lower the oxygen content in the spatial atmosphere of theenclosed room 2 from its original 17.4% by volume to 17.0% by volume.How long the compressor or compressors 3.1, 3.2, 3.3 need to run inorder to lower the oxygen content in the spatial atmosphere of theenclosed room 2 from its original 13.4% by volume to 13.0% by volumewith the inerting system 1 according to FIGS. 1 to 4 is then alsodepicted on the other hand.

The comparison of the two drawdown times (drawdown time control of17.4%→17.0% by volume and drawdown time control of 13.4%→13.0% byvolume) shows that to set and maintain an inerting level of 17.0% byvolume, the runtime of compressor 3.1, compressors 3.1, 3.2, 3.3respectively, can be minimized when a nitrogen purity of approx. 93.3%by volume is set at the gas separation system. However, to set andmaintain an inerting level of 13% by volume oxygen content, thetime-optimized purity will then be about 94.1% nitrogen by volume. Hencethe drawdown time or the runtime of compressor 3.1 or compressors 3.1,3.2, 3.3 respectively for setting a predefined inerting level in thespatial atmosphere of enclosed room 2 is dependent upon the nitrogenpurity set for the gas separation system, or respectively dependent uponthe residual oxygen content of the nitrogen-enriched gas mixtureprovided at the outlet of the gas separation system as set by means ofthe nitrogen generators 4.1, 4.2, 4.3 employed.

The respective minima of the drawdown time relative the nitrogen purityis referred to in the following as “time-optimized nitrogen purity.” TheFIG. 6 depiction shows the optimized nitrogen purity for the inertingsystem 1 according to FIGS. 1 to 4. Specifically indicated is thetime-optimized purity which applies to the gas separation system of theinerting system 1 according to FIGS. 1 to 4 for the different oxygenconcentrations in the spatial atmosphere of enclosed room 2.

It can be directly seen from the characteristic curve depicted in FIG. 6that the nitrogen generators 4.1, 4.2, 4.3 employed are to be set suchthat the residual oxygen content in the gas mixture provided at theoutlet of the gas separation system decreases with decreasing oxygencontent in the spatial atmosphere of enclosed room 2. When the employednitrogen generator is accordingly operated pursuant the nitrogen puritycharacteristic curve depicted in FIG. 6 when rendering enclosed room 2inert, it is possible to set and maintain the predefined inerting levelin the spatial atmosphere of enclosed room 2 at the shortest possibleruntime of the compressors 3.1, 3.2, 3.3 as employed and thus at thelowest possible expenditure of energy.

FIG. 7 provides a graphical depiction of the influence the oxygencontent in the initial gas mixture has on the gas separation system airfactor. According thereto, at a fixed nitrogen purity for the gasseparation system, the air factor drops as the oxygen content is reducedin the initial gas mixture. As noted above, the return supply line 9 isprovided in the inerting system 1 according to the schematic depictionof e.g. FIG. 1, by means of which a portion of the room's ambient air(already nitrogenated where applicable) is fed to the mixing chamber 6in regulated manner so as to thus reduce the oxygen content of theinitial gas mixture from its original 21% by volume (the oxygen contentof normal ambient air). This recirculating of the room's alreadynitrogenated air can thus further reduce the air factor of the gasseparation system so that the efficiency of the gas separation systemwill be increased and the energy required to set and maintain apredefined inerting level can be even further reduced.

The characteristic curve depicted in FIG. 7 can preferably be combinedwith the method graphically represented by FIGS. 5 and 6 such that anoptimized supply of nitrogen is provided for each initial gas mixtureoxygen concentration and in room 2.

FIG. 8 depicts—for a calculated application—the energy savings which canbe achieved (in %) with the oxygen content set in the spatial atmosphereof an enclosed room when the inventive solution lowers the oxygenconcentration in the spatial atmosphere of the enclosed room. The casedepicted here is one in which the time-optimized nitrogen purity wasselected for the nitrogen generator's nitrogen purity during theinerting of the room on the one hand and, on the other, the previouslynitrogenated room air was recirculated so as to thereby further reducethe nitrogen generator's air factor and increase its efficiency.

A fifth exemplary embodiment of the inventive inerting system 1 will bedescribed in the following with reference being made to the depictionprovided in FIG. 9.

The design and functioning of the inerting system 1 according to thefifth embodiment is essentially identical to that of the fourthembodiment described above with reference to FIG. 4. The nitrogengenerator 4.3 of the plurality of nitrogen generators 4.1, 4.2. and 4.3connected in parallel is designed in this fifth embodiment as a vacuumpressure swing adsorption generator based on VPSA technology. Aspreviously described referencing the fourth embodiment according to FIG.4, the vacuum pressure swing adsorption generator 4.3 according to thefifth embodiment is also connected by means of a line system 17.3 to anassociated compressor 3.3 which in turn has a connection to the mixingchamber 6 via a line system 15.3. An intermediate valve is additionallylooped into the line system 17.3 between the compressor 3.3 and thevacuum pressure swing adsorption generator 4.3 which is designed so asto be controllable and has a connection to the control unit 5 for thispurpose. Additionally to the connection made between the mixing chamber6 and the vacuum pressure swing adsorption generator 4.3 through acompressor 3.3, a further line system 42 is provided between the mixingchamber 6 and the generator 4.3. An intermediate valve is again loopedinto this additional line system 42 which is likewise designed so as tobe controllable and has a connection to the control unit 5 for thispurpose.

The control unit 5 itself is designed so as to keep the intermediatevalve 40 between the compressor 3.3. and the generator 4.3 in an openposition during adsorption operation of the vacuum pressure swingadsorption generator 4.3 and to keep the intermediate valve 41 betweenthe mixing chamber 6 and the generator 4.3 in a closed position duringsuch adsorption operation of the generator 4.3. During desorptionoperation of the vacuum pressure swing adsorption generator 4.3 havingat least one inlet, the correspondingly designed associated compressor3.3. creates a negative pressure at the at least one inlet of thegenerator 4.3; i.e. a pressure which is reduced to approaching vacuumcompared to the ambient pressure. During this desorption phase, thecontrol unit 5 then opens the intermediate valve 41 between the mixingchamber 6 and the generator 4.3, preferably a few seconds, andparticularly preferred five seconds, prior to the scheduled end of thedesorption phase so that nitrogen-enriched air can flow though the linesystem 42 directly from the mixing chamber 6 into the at least inlet ofthe vacuum pressure swing adsorption generator 4.3 before the desorptionphase ends. To prevent an obstructing of the influx and interaction withthe compressor 3.3, it can then be provided for the intermediate valve40 between the compressor 3.3 and the generator 4.3 to be brought into aclosed position during this pressure equalization process. The passiveinflux of the nitrogen-enriched air from the mixing chamber into the atleast one inlet of the generator 4.3; i.e. not induced by the associatedcompressor 3.3, then undergoes an increase in pressure prior to the endof the desorption phase at the inlet and within the generator 4.3 to nomore than the pressure inside the mixing chamber 6, which occursrelatively rapidly due to bypassing the compressor 3.3 and moreover doesnot require any energy-intensive operation of the associated compressor3.3 during said pressure equalization process.

In a subsequent adsorption phase of the vacuum pressure swing adsorptiongenerator 4.3, the associated compressor 3.3 can then bring thegenerator 4.3 to its operating pressure in a shorter amount of time,whereby the adsorption and thus the providing of nitrogenated air inturn commences earlier. Because the air from mixing chamber 6 used inthe pressure equalization is already nitrogenated, the oxygen level inthe subsequent adsorption phase of the generator 4.3 starts out lower.

The vacuum pressure swing adsorption generator 4.3 is hereby not limitedto one inlet, one single molecular sieve bed respectively, equipped asapplicable with a container containing carbon granule. It is insteadalso conceivable to provide a separate controllable intermediate valve41 in front of each container, respectively in front of each inlet ofthe vacuum pressure swing adsorption generator 4.3; i.e. a branching ofthe line system 42 between the mixing chamber 6 and the generator 4.3prior to the respective inlets. This thereby enables the alternatingadsorption/desorption operation of a vacuum pressure swing adsorptiongenerator 4.3 so that the most continuous flow of nitrogen-enriched airpossible will be provided at its inlet 4 a.3 for feeding into theenclosed room 2.

The mixing chamber 6 is preferably designed as a comparatively longmixing tube and the outgoing line systems 15.1, 15.2, 15.3 toward thecompressors 3.1, 3.2, 3.3 then branch off from the end of such a mixingtube. The appropriate dimensioning of a mixing chamber 6, in particularsuch a relatively long mixing tube, then ensures an operation which islargely non-interacting even when this type of a passive pressureequalization process uses an additional line system 42 between themixing chamber 6 and the vacuum pressure swing adsorption generator 4.3.In other words, the appropriate dimensioning of such a mixing chamber 6configured as a long mixing tube reduces the pressure influence; i.e.the pressure effect on the nitrogen generators 4.1, 4.2, to a harmlessvalue, even when using a vacuum pressure swing adsorption generator 4.3equipped with a bypass line 42.

In contrast to this fifth embodiment depicted in FIG. 9, such anadditional line 42 between the mixing chamber 6 and a vacuum pressureswing adsorption generator 4.3 through the intermediary connection of acorrespondingly controllable intermediate valve 41 can then however alsobe an advantage in the absence of a great plurality of gas separationsystems 3.1, 4.1; 3.2, 4.2; 3.3, 4.3 or when nitrogen generators 4.1,4.2, 4.3 utilizing different gas separation techniques are not employed.Even just providing one vacuum pressure swing adsorption generator 4.3yields the advantage that, given the appropriate dimensioning of themixing chamber 6, the passive pressure equalization can be regulated bythe intermediate valve 41 prior to the end of the desorption phase ofthe vacuum pressure swing adsorption generator 4.3 allows the associatedcompressor 3.3 to be operated for a shorter amount of time in total,thereby providing an energy-saving effect.

A sixth exemplary embodiment of the inventive inerting system 1 will bedescribed in the following with reference being made to the depictionprovided in FIG. 10.

The design and functioning of the inerting system 1 according to thesixth embodiment is essentially comparable to the fifth embodimentdescribed above with reference to the FIG. 9 depiction. As in theabove-described fifth embodiment, the nitrogen generator 4.3 of theplurality of nitrogen generators 4.1, 4.2 and 4.3 connected in parallelis likewise configured in this sixth embodiment as a vacuum pressureswing adsorption generator based on VPSA technology. The vacuum pressureswing adsorption generator 4.3 in accordance with the sixth embodimentis also connected by means of a line system 17.3 to an associatedcompressor 3.3 which in turn has a connection to the mixing chamber 6via line system 15.3. The vacuum pressure swing adsorption generator 4.3further exhibits an additional inlet directly connected to the mixingchamber 6 by way of an additional line system 42. The nitrogen generator4.3 configured as a vacuum pressure swing adsorption generatoradditionally comprises two independently operable adsorption beds 45 aand 45 b which are connected by way of a respective controllableintermediate valve 44 a/44 b to an inlet 4 a.3 of the nitrogen generator4.3 which in turn can supply the enclosed room 2 with nitrogen-enrichedair through a supply line 7.3. A plurality of additional intermediatevalves 40 a, 41 a, 43 a, respectively 40 b, 41 b, 43 b, are provided foreach of the molecular sieve beds 45 a/45 b in the area of the respectivemolecular sieve bed inlets. All of these intermediate valves aredesigned to be controllable and can be correspondingly actuated togetherwith the additional intermediate valves 44 a, 44 b such that the firstmolecular sieve bed 45 a is operated in an adsorption mode during afirst respective time period so as to supply the supply line 7.3 withnitrogenated air. During a second period, the second molecular sieve bed45 b is then operated in such an adsorption state as to likewise supplythe supply line 7.3 with nitrogenated air. In other words, by means ofthe respectively alternating adsorption/desorption operation of themolecular sieve beds 45 a, 45 b, a vacuum pressure swing adsorptiongenerator 4.3 designed as such enables a continuous flow of nitrogenatedair output in the supply line 7.3.

During the adsorption operation of the first molecular sieve bed 45 a ofthe vacuum pressure swing adsorption generator 4.3, the intermediatevalve 40 a between the inlet of the nitrogen generator 4.3 connected tothe compressor 3.3. by means of line system 17.3 as well as theassociated intermediate valve 44 a which regulates the outlet are openedso that nitrogenated air is provided at the outlet 4 a.3 of the nitrogengenerator 4.3. Intermediate valve 40 b is accordingly closed during suchadsorption operation of the first molecular sieve bed 45 a of thenitrogen generator 4.3 in order to not subject the second molecularsieve bed 45 b to compressed air from the compressor 3.3. The secondmolecular sieve bed 45 b is operated in desorption mode during thistime, with the intermediate valve 43 b being open so as to connect thesecond molecular sieve bed 45 b to the vacuum source V. Intermediatevalves 43 a and 44 b are accordingly closed in this operating mode.Likewise closed are intermediate valves 41 a and 41 b which canestablish a connection to the further line system 42 and thus to mixingchamber 6.

If the nitrogen generator 4.3 configured as a pressure swing adsorptiongenerator is now switched from this operating mode; i.e. from theoperating mode in which the first molecular sieve bed 45 a is operatedin adsorption mode and the second molecular sieve bed 45 b is operatedin desorption mode, to a reversed operating mode in which the firstmolecular sieve bed 45 a is operated in desorption mode and the secondmolecular sieve bed 45 b is operated in adsorption mode, then shortlybefore the point in time at which the desorption mode of the secondmolecular sieve bed 45 b is to be ended, the intermediate valves 40 a,40 b and 43 a, 43 b as well as the intermediate valves 44 a, 44 barranged as applicable on the outlet side, are closed. At the same timeor directly thereafter, intermediate valve 41 b is then opened in orderto create a direct connection between the mixing chamber 6 and thesecond molecular sieve bed 45 b via the additional line system 42. Thisresults in a passive equalizing of the pressure prevailing within thesecond molecular sieve bed 45 b, whereby air which is alreadynitrogenated passively flows from the mixing chamber 6 to the secondmolecular sieve bed 45 b in advantageous manner. After the pressure hasbeen equalized, intermediate valve 41 b can be closed again andintermediate valve 40 b opened to connect the compressor 3.3 to theinlet of the second molecular sieve bed 45 b to initiate the adsorptionphase in the second molecular sieve bed 45 b. In corresponding manner,the outlet-side intermediate valve 44 b to provide nitrogenated air atthe outlet 4 a.3 of the nitrogen generator is opened. At this point, thefirst molecular sieve bed 45 a can operate in desorption mode, with onlythe intermediate valve 43 a, which connects the inlet of the firstmolecular sieve bed 45 a to the vacuum source, needing to be open.

In similar manner, switching this nitrogen generator 4.3 operating withtwo molecular sieve beds from an operating mode in which the firstmolecular sieve bed 45 a is in desorption mode and the second molecularsieve bed 45 b is in adsorption mode with the intermediary step ofpassive pressure equalization occurring to end the desorption phase inthe first molecular sieve bed 45 a.

The invention is not limited to the embodiments shown by way of therepresentations provided in the accompany drawings but instead yieldsfrom a synopsis of all the features disclosed herein. In conjunctionhereto, it is in particular to be noted that the drawings do not providea detailed depiction of obvious features which are not essential to theinvention. For instance, the drawings do not show the outlet for theoxygenated gas of the respective nitrogen generators 4.1, 4.2, 4.3.Providing a correspondingly designed control unit 5 and appropriatelyconnecting it to the individually controllable elements such as e.g. theintermediate valves can likewise be provided in the sixth embodimentaccording to FIG. 10.

LIST OF REFERENCE NUMERALS

-   1 inerting system-   2 enclosed room-   3.1, 3.2, 3.3 compressor-   4.1, 4.2, 4.3 nitrogen generator-   4 a.1, 4 a.2, 4 a.3 nitrogen generator outlet-   5 control unit-   6 mixing chamber-   7.1, 7.2, 7.3 supply line-   8 (fresh air) supply line-   8 a fresh air supply line inlet-   9 return line-   9 a return line inlet-   10 second fan mechanism-   11 first fan mechanism-   12 mixing section-   13 heat exchanger system-   14 booster fan-   15.1, 15.2, 15.3 line system between mixing chamber and compressor-   16 oxygen measuring system-   17.1, 17.2, 17.3 line system between compressor and nitrogen    generator-   18 filter-   19 membrane module-   20 thermal insulation-   21 residual oxygen content measuring system-   23 oxygen measuring system in return line 9-   24 oxygen measuring system in supply line 8-   25 external area-   26 pressure sensor in mixing chamber-   27 pressure sensor in external area-   28.1, 28.2, 28.3 volumetric flow sensor in supply line 7.1, 7.2, 7.3-   29 volumetric flow sensor in return line 9-   30 volumetric flow sensor in fresh air supply line 8-   40, 40 a, 40 b intermediate valve between compressor and molecular    sieve bed inlet-   41, 41 a, 41 b intermediate valve between mixing chamber and    molecular sieve bed inlet-   42 line system between mixing chamber and nitrogen generator-   43 a, 43 b intermediate valve between vacuum source and molecular    sieve bed inlet-   44 a, 44 b intermediate valve between molecular sieve bed outlet and    supply line-   45 a, 45 b molecular sieve bed and vacuum source V

What is claimed is:
 1. An inerting system (1) to set and/or maintain apredefinable oxygen content in the spatial atmosphere of an enclosedroom (2) which is reduced compared to the normal ambient air, theinerting system comprising: a gas separation system (3.1, 4.1; 3.2, 4.2;3.3, 4.3) which separates off at least a portion of the oxygen from aninitial gas mixture containing nitrogen and oxygen and by so doing,provides a nitrogen-enriched gas mixture at an outlet (4 a.1; 4 a.2; 4a.3) of the gas separation system (3.1, 4.1; 3.2, 4.2; 3.3, 4.3); asupply line system (7) for supplying the nitrogen-enriched gas mixtureto the enclosed room (2); a mixing chamber (6) configured as a mixingtube configured to provide the initial gas mixture; a first line system(9) through which a portion of spatial air contained in the enclosedroom (2) is withdrawn and fed to said mixing chamber (6), the first linesystem (9) opening into the mixing chamber (6); a second line system (8)through which fresh air is supplied to the mixing chamber (6), thesecond line system (8) opening into said mixing chamber (6); a controlunit (5); a first fan mechanism (11) in the first line system (9) andcontrollable via the control unit (5); and a second fan mechanism (10)in the second line system (8) and controllable via the control unit (5).2. The inerting system (1) according to claim 1, wherein the controlunit (5) is designed so as to control the first fan mechanism (11) suchthat the amount of air withdrawn from the room (2) per unit of time andfed to the mixing chamber (6) via said first fan mechanism (11) can beset such that the difference between the pressure prevailing in themixing chamber (6) and the pressure of the external ambient atmospheredoes not exceed a predefined or predefinable upper threshold nor fallshort of a predefined or predefinable lower threshold.
 3. The inertingsystem (1) according to claim 1, wherein the control unit (5) isdesigned so as to control the second fan mechanism (10) such that thevolume of fresh air admixed to the withdrawn spatial air per unit oftime via said second fan mechanism (10) can be set such that thedifference between the pressure prevailing in the mixing chamber (6) andthe pressure of the external ambient atmosphere does not exceed apredefined or predefinable upper threshold nor fall short of apredefined or predefinable lower threshold.
 4. The inerting systemaccording to claim 1, whereby the control unit (5) is further configuredto control the gas separation system (3.1, 4.1; 3.2, 4.2; 3.3, 4.3) suchthat the residual oxygen content of the nitrogen-enriched gas mixture ischanged as a function of the oxygen content prevailing at thatrespective moment in the spatial atmosphere of the enclosed room (10).5. The inerting system (1) according to claim 1, wherein the first fanmechanism (11) actuatable by the control unit (5) is further comprisedin the first line system (9) and the second fan mechanism (10)actuatable by the control unit (5) is provided in the second line system(8), wherein the control unit (5) is designed to control the firstand/or second fan mechanism (10, 11) such that the volume of spatial airwithdrawn from the room (2) per unit of time is identical to the volumeof the nitrogen-enriched gas mixture which is supplied to the spatialatmosphere of the enclosed room (2) per unit of time.
 6. The inertingsystem (1) according to claim 1, wherein the inerting system (1) furthercomprises a mixing section (12) either integrated in the mixing chamber(6) or provided upstream of the mixing chamber (6) into which opens thefirst and the second line system (9, 8), via a Y-connector, wherein themixing section (12) is configured particularly with respect to itseffective flow cross section such that a turbulent flow will occur inthe mixing section (12).
 7. The inerting system (1) according to claim6, wherein the mixing section (12) is of a length which is at least fivetimes a hydraulic diameter of the mixing section (12).
 8. The inertingsystem (1) according to claim 1, wherein the gas separation system (3.1,4.1; 3.2, 4.2; 3.3, 4.3) comprises at least one nitrogen generator (4.1,4.2, 4.3) associated with at least one compressor (3.1, 3.2, 3.3) of thegas separation system (3.1, 4.1; 3.2, 4.2; 3.3, 4.3) and connected tothe mixing chamber (6) via a line system (15.1, 15.2, 15.3) comprised bythe inerting system (1).
 9. The inerting system (1) according to claim8, wherein a residual oxygen content of the nitrogen-enriched gasmixture provided at an outlet (4 a.1, 4 a.2, 4 a.3) of the at least onenitrogen generator (4.1, 4.2, 4.3) of the gas separation system (3.1,4.1; 3.2, 4.2; 3.3, 4.3) can be set at each of the at least one nitrogengenerator (4.1, 4.2, 4.3) via the control unit (5).
 10. The inertingsystem (1) according to claim 8, wherein the at least one nitrogengenerator (4.3) is configured as a vacuum pressure swing adsorptiongenerator, and wherein at least one vacuum source (V) is provided towhich at least one inlet of the nitrogen generator (4.3) configured as avacuum pressure swing adsorption generator can be connected.
 11. Theinerting system (1) according to claim 8, wherein the at least onenitrogen generator (4.3) is configured as a vacuum pressure swingadsorption generator and wherein the inerting system (1) additionallycomprises a line system (42) via which at least one inlet of thenitrogen generator (4.3) configured as a vacuum pressure swingadsorption generator can be connected to the mixing chamber (6).
 12. Theinerting system (1) according to claim 1, wherein the mixing chamber (6)exhibits a volume which is dependent on the number of nitrogengenerators (4.1, 4.2, 4.3) used in the inerting system (1) and/or on theprinciple on which the functioning of the least one nitrogen generator(4.1, 4.2, 4.3) is based.
 13. The inerting system (1) according to claim1, wherein the hydraulic cross section of the mixing chamber (6) is atleast large enough that the maximum flow rate which can occur in themixing chamber (6) is less than 0.1 m/s on average.
 14. The inertingsystem (1) according to claim 1, wherein the control unit (5) is furtherconfigured to control the gas separation system (3.1, 4.1;3.2, 4.2; 3.3,4.3) as a function of the oxygen content prevailing at the respectivemoment in the spatial atmosphere of the enclosed room (2) such that theresidual oxygen content of the nitrogen-enriched gas mixture provided atthe outlet (4 a.1; 4 a.2; 4 a.3) of the gas separation system (3.1, 4.1;3.2, 4.2; 3.3, 4.3) automatically decreases as the oxygen content in thespatial atmosphere of the enclosed room (2) decreases.
 15. The inertingsystem (1) according to claim 1, wherein the control unit (5) is furtherconfigured to set the volume of the spatial air withdrawn from the room(2) per unit of time and fed to the mixing chamber (6) and the volume offresh air admixed to the withdrawn room air per unit of time as afunction of the oxygen content prevailing at that respective moment inthe spatial atmosphere of the enclosed room (2) such that the initialgas mixture provided by the mixing chamber (6) exhibits a predefinableoxygen content which is dependent on the oxygen content prevailing inthe spatial atmosphere of the enclosed room (2) at that respectivemoment.
 16. The inerting system (1) according to claim 1, wherein thecontrol unit (5) is configured for at least: providing the initial gasmixture containing oxygen, nitrogen and other components as applicablein the mixing chamber configured as the mixing tube; providing the gasseparation system (3.1, 4.1; 3.2, 4.2; 3.3, 4.3) separating off at leasta portion of the oxygen from this initial gas mixture provided and by sodoing, providing the nitrogen-enriched gas mixture at the outlet (4 a.1;4 a.2; 4 a.3) of the gas separation system (3.1, 4.1; 3.2, 4.2; 3.3,4.3); and piping the nitrogen-enriched gas mixture into the spatialatmosphere of the enclosed room (2), wherein providing the initial gasmixture comprises using a fan mechanism (11) provided in a return linesystem (9) as the first line system connecting the enclosed room (2) tothe mixing chamber (6), a portion of the ambient air contained withinthe enclosed room (2) is withdrawn from the room (2) in regulatedmanner, and fed to the mixing chamber (6), and the withdrawn portion ofthe room's air is mixed with fresh air in a regulated manner, via thesecond fan mechanism (10) provided in a fresh air supply line system (8)as the second line system connected to the mixing chamber (6).